1. Field of the Invention
The invention relates to a process for the treatment of a cellulosic molded body.
In particular, the invention relates to a process for modifying the properties of cellulosic molded bodies using chitosan.
2. Description of Related Art
Chitin and chitosan are natural, biodegradable, non-toxic, non-allergenic, bioactive and biocompatible polymers with a structure similar to that of cellulose. Chitin is obtained from the shells of crustaceans, a waste material of the crab and shrimp industries. The worldwide interest in the possible uses of chitin has seen an enormous increase in recent years as it is regarded as the second largest resource of natural polysaccharides beside cellulose.
Chitosan consists of poly-(1,4)-2-amino-2-desoxy-beta-D-glucose and is produced by deacetylation of chitin (poly-(1,4)-2-acetamide-2-desoxy-beta-D-glucose). For reasons of solubility—chitin is insoluble in water, organic solvents, diluted acids and bases—chitosan, which is soluble in diluted acids, aqueous methanol and glycerol, has the by far greater significance.
Areas of application for chitin and chitosan are the immobilization of cells and enzymes in biotechnology, the treatment of wounds in medicine, the use as nutritional supplement and preserving agent in the food industry, the preservation of seeds in agriculture, and the use as flocculating agent and chelating agent with heavy metals in sewage systems.
However, a modification of chitin/chitosan has to be carried out for most areas of application in order to improve the solubility in aqueous systems.
The use of chitosan in the textile industry is divided into three fields of application:                the production of 100% chitosan fibers and the production of “man-made fibers” with incorporated chitosan, respectively        the finishing and coating of textile fibers        auxiliary process agents for the textile industry        
Due to their antibacterial properties and inhibitory effects on the growth of pathogenic germs, chitosan fibers are used in the field of medicine, e.g., as wound coverage and surgical sutures. Chitin and chitosan, respectively, can be broken down enzymatically or hydrolytically by endogenic ferments and therefore are reabsorbable. The effect of such natural polymers on the healing of wounds consists in the gradual release of N-acetyl-glucosamine, the mucopolysaccharide organization of the collagen as well as the beneficial effect on the tissue growth during wound healing (EP 0 077 098, U.S. Pat. No. 4,309,534, JP81/112937, JP84/116418 and many more).
The disadvantage of fibers made of 100% chitosan, however, consists in that they exhibit low dry strength (chitosan fibers of Innovative Technology Ltd., Winsford, England: titer 0.25 tex; fiber strength conditioned 9 cN/tex; fiber elongation conditioned 12.4%; chitosan fibers of Korea Chitosan Co. LTD: fiber strength conditioned 15 cN/tex; fiber elongation conditioned 26%), that they are extremely brittle and that the wet strength amounts to merely 30% of the dry strength. Therefore, either chitosan fibers are admixed to other man-made fibers, or chitosan is added to the spinning mass during the manufacturing process of, e.g., viscose fibers.
Viscose fibers with incorporated chitin/chitosan (in the following: “chitosan-incorporated viscose fibers”) are commercially available, e.g., under the trade names Crabyon (Omikenshi Co) and Chitopoly (Fuji Spinning Co.). Those fibers are produced, for instance, by dispersing chitosan or acetylated chitosan in powder form with a grain size of below 10 μm in water in an amount of from 0.5 to 2% by weight and by adding it to the viscose dope (U.S. Pat. No. 5,320,903). Thereupon, fibers are produced in accordance with the conventional viscose process or the polynosic process.
Further manufacturing processes for chitosan-incorporated viscose fibers are described in U.S. Pat. No. 5,756,111 (complex pre- and post-dissolution processes at low temperature in order to obtain alkaline chitin-chitosan solutions to be added to the viscose solution), in U.S. Pat. No. 5,622,666 (addition of microcrystalline chitosan and a water- and/or alkali-soluble natural polymer, e.g., sodium alginate, which can form ionic bonds with the chitosan, as a dispersion to the viscose dope) and in PCT/FI90/00292 and FI 78127, respectively (addition of microcrystalline chitosan to the spinning mass).
The chitosan-incorporated viscose fibers exhibit an increased dye affinity, an increased water retention value, fungicidal and odor-reducing properties, and also the low wet strength viscose fibers are known for. Since chitosan prevents the growth of bacteria harmful to the skin and eliminates allergic effects, for instance, fabrics made of Chitopoly are particularly suitable for dermatitis patients.
The drawback of all the methods described consists in that the fibers thus obtained contain very fine chitosan particles, since the chitosan is not soluble in the spinning mass.
The secondary agglomeration of the chitosan in the spinning mass or the inhomogeneous distribution, respectively, results in a deterioration of the spinning properties, spinning of fibers with low titers is extremely difficult. For that reason, it is also difficult to increase the amount of incorporated chitosan, since, in doing so, there would be an immediate loss of textile data or, during spinning, numerous fiber breakages would occur. Furthermore, leakages of chitosan occur in the spinning bath, since chitosan is soluble in acids. For the incorporation of chitosan, additional complex steps are necessary.
Furthermore, in order to ensure the effect of the chitosan in the final product, an amount of at least approximately 10% by weight of chitosan has to be incorporated into the fibers, since only then there will be sufficient chitosan on the fiber surface. That is to say, the chitosan incorporated in the interior of the fibers is inaccessible and thus ineffective.
Subsequently, it also was attempted to incorporate chitosan in solvent-spun cellulose fibers produced in accordance with the amine-oxide process (so-called “lyocell fibers”), in particular, because of the high wet and dry strength of lyocell fibers.
In DE 195 44 097, a process for the production of molded bodies from polysaccharide mixtures is described, wherein cellulose and a second polysaccharide are dissolved in an organic polysaccharide solvent mixable with water (preferably NMMO), which may also contain a second solvent.
Furthermore, in KR-A 9614022, the production of chitin-cellulose fibers, referred to as “chitulose”, is described, wherein chitin and cellulose are dissolved in a solvent from the group comprising dimethylimidazoline/LiCl, dichloroacetate/chlorinated hydrocarbon, dimethylacetamide/LiCl, N-methylpyrrolidone/LiCl, and yarns are produced according to the wet spinning process. NMMO is not mentioned in the claims.
In EP-A 0 883 645, among other things, the addition of chitosan to the solution as a modified compound for increasing the elasticity of wraps for foodstuff is claimed. The modifying compounds must be miscible with the cellulose/NMMO/water solution.
KR-A-2002036398 describes the incorporation of chitosan derivatives with quaternary ammonium groups into fibers, which are produced in a complex manner.
In DE-A 100 07 794, the production of polymer compositions is described, comprising a biodegradable polymer and a material consisting of sea weed and/or the shells of sea animals, as well as the production of molded bodies therefrom. The addition of a material made of sea weed, sea animals in powder form, in the form of a powder suspension or in liquid form to the cellulose solution produced according to the lyocell process is also claimed. Furthermore, the material may also be added after or during the shredding of the dry cellulose as well as at any stage of the manufacturing process. Despite the addition of the additive, the fibers exhibit the same textile-mechanical properties as they would without the additive. In the examples, only lyocell fibers that have a brown algae powder incorporated are described, wherein, for the production of the spinning mass, the brown algae powder, NMMO and pulp and a stabilizer are mixed and heated to 94° C.
Furthermore, in the final report “Erzeugnisse aus Polysaccharidverbunden” (Taeger, E.; Kramer, H.; Meister, F.; Vorwerg, W.; Radosta, S; TITK—Thüringisches Institut für Textil-und Kunststoff-Forschung, 1997, pp. 1-47, report no. FKZ 95/NR 036 F) it is described that chitosan is dissolved in diluted organic or inorganic acids and then is precipitated in an aqueous NMMO solution. Thus, a suspension of fine chitosan crystals is obtained in the cellulose solution, which then is spun. According to said document, the chitosan remains in the solution in the form of fine crystals even after the dissolution of the cellulose. That leads to the formation of a microheterogeneous two-phase system in the fiber. The strength of the fiber is low (with 10% chitosan: fiber strength conditioned 19.4 cN/tex; fiber elongation conditioned 11.5%).
In WO 04/007818, it is suggested that a chitosonium polymer (a salt of chitosan with an inorganic or organic acid) soluble in the spinning dope be incorporated into the lyocell fiber by adding it to the dope or to a precursor thereof.
As an alternative to the incorporation, the possibility exists to furnish textile assemblies with chitosan in the course of the manufacture. The application of chitosan onto fibers which have already been produced or onto textile articles containing those fibers is subsequently also referred to as “impregnation”. However, a basic problem associated therewith is that the chitosan applied in this manner is not fixed and is washed out relatively quickly, whereby the positive effects are lost.
In order to avoid this problem, the use of chitosan nanoparticles for the production of fibers, yarns, knitted fabrics and textile assemblies is suggested in EP 1 243 688. “Nano-chitosans” are understood to be roughly spherical solid bodies which have an average diameter ranging from 10 to 300 nm and, due to the small particle diameter, are incorporated between fibrils. The production of nano-chitosans is effected by spray drying, evaporation technique or expansion of supercritical solutions.
In WO 01/32751, a process for the production of nanoparticulate chitosan for cosmetic and pharmaceutical preparations with particle diameters of from 10 to 1000 nm is described, wherein the pH-value of an aqueous acidic chitosan solution is increased in the presence of a surface modifying agent to such an extent that the chitosan will precipitate. Furthermore, in WO 91/00298, the production of microcrystalline chitosan dispersions and powders with particle diameters of from 0.1 to 50 μm is described, wherein the pH-value of an aqueous acidic chitosan solution is increased to such an extent that the chitosan will precipitate.
WO 97/07266 describes the treatment of a lyocell fiber with an acetous 0.5% chitosan solution.
In WO 2004/007818, in addition to the incorporation of a chitosonium polymer into lyocell fibers, also the treatment of never-dried lyocell fibers with the solution or suspension of a chitosonium polymer is described. It has been shown that said process is suitable only for the treatment of never-dried lyocell fibers.
The term “never-dried” thereby describes the state of a freshly spun fiber which has not yet been subjected to a drying step.
A treatment of fiber types other than lyocell fibers in the never-dried state is not possible by means of the process according to WO 2004/007818.